Senior British and Irish officials have traded barbs on Twitter after Britain's Brexit negotiator restated that the EU must agree "significant change" to the Northern Ireland protocol governing trade and border rules there.
The protocol was part of the Brexit settlement Prime Minister Boris Johnson negotiated with the EU.
However Britain has repeatedly said it must be rewritten less than a year after taking force due to the barriers businesses face when importing British goods into Northern Ireland.
Ireland Foreign Minister Simon Coveney on Twitter asked: "Real Q: Does UKG (UK government) actually want an agreed way forward or a further breakdown in relations?"
That drew a rebuke from British Brexit negotiator David Frost: "I prefer not to do negotiations by twitter, but since @simoncoveney has begun the process..."
Frost dismissed Coveney's argument that he was making new demands, saying Britain's concerns over the European Court of Justice's role in the process were set out three months earlier.
"The problem is that too few people seem to have listened," Frost said.
On Saturday, Frost released extracts of a speech he is due to make this week again calling for change and signalling a desire to free the protocol from the oversight of European judges.
Responding to that, Ireland's Coveney said Britain had created a new "red line" barrier to progress that it knows the EU cannot move on.
The row comes at the start of an important week in the long running debate over how to manage the flow of goods between Britain, Northern Ireland and the EU.
The European Commission is expected to present new measures on Wednesday aimed at resolving post-Brexit trading issues, but has repeatedly stated it is not willing to renegotiate the protocol.